As a method for realizing high-speed signal transmission within a single electronic device or between electronic devices arranged with a relatively short distance (e.g., within several centimeters or ten-odd centimeters) therebetween, LVDS (Low Voltage Differential Signaling) is known, for example. However, with a recent further increase in the volume and speed of transmission data, the following problems would arise: increased power consumption, increased influence of signal distortion due to reflections and the like, increased unwanted radiation, and the like. For example, when video signals (including image signals) or signals of computer images or the like are transmitted at high speed (in real time) within a device, LVDS has been reaching its limit.
In order to cope with the problems with the increased speed of transmission data, there is a method of increasing the number of wires and parallelizing signals to reduce the transmission rate per signal line. However, this could result in an increased number of input/output terminals. Consequently, it is required to make a printed board or cable wires more complex, increase the semiconductor chip size, and the like. Further, when high-speed, large-volume data is routed using wires, a problem of so-called electromagnetic field disturbance would arise.
All of the problems with the LVDS and the method of increasing the number of wires are attributable to the transmission of signals by electrical wires. Therefore, as a method for solving the problems attributable to the transmission of signals by electrical wires, a method of making electrical wires wireless for transmission is proposed.
For example, JP 2005-204221A and JP 2005-223411A each propose performing wireless signal transmission within a housing and adopting a UWB (Ultra Wide Band) communication method. The UWB communication method described in the two patent literatures uses a low carrier frequency and thus is not suitable for high-speed communication for transmitting video signals, for example. In addition, there is a problem in size such as an increased antenna size. Further, as the frequency used for transmission is close to the frequency of the other baseband signal processing, there is a problem in that interference is likely to occur between a wireless signal and a baseband signal. Furthermore, when the carrier frequency is low, it will be more susceptible to the influence of noise of a drive system within the device. Thus, measures against it should be taken.
In contrast, JP H10-256478A and U.S. Pat. No. 5,754,948A each describe using a carrier frequency of a millimeter-wave band. As described in the two patent literatures, when a carrier frequency of a millimeter-wave band with a shorter wavelength is used, the problems of the antenna size and the influence of noise of a drive system could be solved.
Citation ListPatent LiteraturePatent Literature 1:JP 2005-204221APatent Literature 2:JP 2005-223411APatent Literature 3:JP H10-256478APatent Literature 4:US 575494A